Field of the Invention and Related Art
The present invention relates to a parallel rule, in particular to a parallel rule having an improved rolling device which reduces the thickness of the rule body and facilitates drawing, and having a gripper body that is easily assembled and disassembled.
A conventional parallel rule is formed by aluminum press work, and rollers are riveted at both ends with one thin steel wire is wound around the rollers.
The rollers are exposed to the outside so the wire can easily be disengaged from the rollers even with a very small movement during drawing work. In addition, the ink of the drawing is easily smeared because the entire surface of the rule is in contact surface of the drawing. Although an improved parallel rule as described in U.S. Pat. No. 4,914,824 employs enclosed type rollers, and has a simpler construction, replacement of the wire or other parts is quite difficult if they are broken during operations. Further, installation of the thin steel wire inside the gripper body is still troublesome because the gripper body is integrally formed and does not allow assess to its interior. In another conventional design, a number of coupling seats are necessary to hold the thin steel wire and rollers in position to provide a float-contact means. This complicated means makes assembly and maintenance work quite difficult. Moreover, the rollers make a great deal of noise when the rule body is moved during drawing because the float-contact means requires several rollers connected in series by the thin steel wire, this noise is a large nuisance for a draftsman. Although it is possible to provide a roller type float-contact means at each end of the rule body as supporting means, if the length of the rule body is comparatively long, the center part of the ruler body may sag so as to prevent the parallel rule from moving easily and to cause it to smear the ink of the drawing. Moreover, the sliding motion of the float-contact means and movement of the parallel rule easily becomes uneven.